Cracking of heavier hydrocarbon oils



'Feb. 2 1929. 1,703,529

E. C. HERTHEL ET AL CRACKING OF HEAVIER HYDROCARBON OILS Filed May 28,1925 7 PIES OIL (lb CONDENSED MPO 4N0 64555 Z0 INVENTORS Eugene C.f/erzheZ vflurry l. PeZzer EwQ IQWZM+M ATTORNEYS Patented Feb. 26, 1929.

UNITED STATES EUGENE C. HERTHEL AND HARRY L. IELZER, OI CHICAGO,ILLINOIS, ASSIGNOBS 'IO PATENT OFFICE.

SINCLAIR REFINING COMIANY, OF CHICAGO, ILLINOIS, A. CORPORATION OFMAINE.

CRACKING 0F HEAVIEB HYDROGARBON': OILS.

Application filed May 28, 1925.

- cation is in part a continuation of our copending application SerialNo. 704,926, fi1ed April 5, 1924, which has issued a Patent 1,634,666.The invention comprises an improved process which assists in protectin,the heating tubes of the cracking still and which also enables thecracking operation to be continued for a prolonged period of time beforethe deposition of carbon begins or before it is necessary to shut downthe cracking still for cleaning pur oses.

In the cra king o heavier petroleum oils in pressure stills for theproduction of gasoline or pressure distillate therefrom there are formedduring the cracking operation certain constituents of an asphaltic orpitch-like character. With continuation'of the crack ing operation, theamount ofsuch constituents increases and there is a tendency for depositof carbon or coke to form on the heated surfaces of the still, thusnecessitating the shutting down of the 'still for cleaning purposesbetween successive runs. The shutting down of a pressure still, thewithdrawal of the charge therefrom, the cleaning of the still, therecharging of thestill and the prelimi nary heating of the still tobring the fresh charge u to cracking conditions, all require time, anthe total amount of time so required in ordinary commercial operationsmeans a corresponding reduction in the proportion of the time when thestill is operating for carrying out the desired cracking operation.

According to the present invention, the deposition of pitch or carbon inthe heating tubes of the pressure still is retarded or reduced so thatoverheating or danger of failme of the heating tubes can be effectivelyprevented, and the time of operation of a single run can be somewhatprolonged, with corre spondingly less loss of time and greaterproduction per still per day. I

When a. pressure still is charged with gas oil or other charging stocktosubjected to Serial No. 38,390.,

cracki'n and when the charge is heated to the crac ring temp.erature,.the crackingtakes place n a gradual and progressive manner. The l1ghterconstituents produced by the cracking operation, which go to make up thepressure distillate, are removed from the still progressively during thecracking operation.

Other. constituents, such as heavier hydrocarbons formed by the crackingoperation,

may remain and mix with the charge of the still. A small amount ofasphaltic or'pitchlike constituents is progressively formed. Suchconstituents appear to be of varying pro erties and characteristics. Forthe most par the 'remain in solution in the charge during t e earlyportion ofthe run, and they may remain completely in solution during the'early portion of the run. With gradual and progressive cracking of thecharge however the amount ofsuch asphalti'c or pitch-like constituentsgradually and progressively increases until sooner or later the amountof such constituents increases beyond the saturation point. Furthermore,certain of these constituents, which appear to be relatively small inamount as compared with the total amount of the pitch-like constituentsformed, appear to be ofa different character and to heating surfaces ofthe still. Furthermore, as the charge becomes supersaturated with theless objectionable pitch-like constituents. there is an increased dangerof de sit of pitch or carbon on the heating sur aces of have anincreased tendency to deposit on the the still, with correspondingdanger of overl heating and failure of the heatedsurfaces w -i if thestill is not shut down at more or less frequent intervals to remove thisdeposit.

Among the constituents produced by the cracking operation which seem tobe. particularly objectionable are certain of the sulfur-containingcompounds. With chargingv Q5 stock which contains. sulfur, certainof'the sulfur compounds appear to undergo ctacking toformsulfur-containing constituents, probably of an asphalt-like character,which are particularly objectionable. Analyses of the carbon deposit onthe heating tubes of a cracking still indicate that certain of thesesulfur-containing constituents have a preferential afiinity for theheated surfaces, or tend to separate out on such surfaces, to give adeposit containing both iron and sulfur in proortions approximatingthose of iron sulde. It may be also that asphalt-like constituents of acolloidal character, or even colloidal carbon, formed as a result of thecracking operation, tend to separate out in the heating tubes of thestill ina preferential manner.

' The present invention relates more particularly to an improved methodof cracking heavier oils in tubular pressure stills in a batch orsemi-continuous operation, and in volves the maintenance within thepressure still of a body of fullers earth in directcontact with thestill charge through which the still charge is circulated during thecracking operation.

We have found that the length of timeduring which the operation of atubular pressure still can be continued can be somewhat prolonged bmaintaining within the pressure still a ody of fullers earth, in directcontact with the still charge, and by causing the still charge tocirculate repeatedly through said body of fullers earth during theprogress of the cracking operation. We have also found that themaintenance of a body of fullers earth within the still charge is ofadvantage in protecting the heating tubes of the still from corrosion,overheating and burning out, and in reducing carbon dep: osition uponthe heating surfaces, whether or not the operation is carried out over aprolonged period.

The bed of fullers earth which is maintained in the still in contact.with the charge, and through which the charge is continuous- 1ycirculated, does not remove from the charge all of the pitch-likeconstituents; but

- it hasa selective action upon certain of these constituents, andapparently removes those constituents which. are particularlyobjectionable from the standpoint of forming a carbon deposit on theheating tubes ofthe still. This selective action may be in part afiltering action, or a selective absorbent action for colloidal carbonor precipitated asphalt-like constituents, or sulfur containingconstituents, etc. Whatever the explanation of the action of the fullersearth may be, it has an important protective eflect in preventingobjectionable carbon deposit. The fact that Without the fullers earththe carbon dc osit contains an important and relatively arge percentageof sulfur, whereas in the process of the present invention suchobjectionable sulfur containing deposit is avoided, or reduced,indicates that the fullers earth has a selective desulphurizing actionupon the pressure still charge, selectively removing therefrom certainof the objectionable sulphur containing constituents of the charge. Itis also probable that constituents of an asphalt-like character producedby the cracking operation and which tend to separate out from the chargeas suspended ever, only the pitch-like constituents whichv are notremoved by the fullers earth bed remain to be held in solution in thecharge, and the fullers earth, in'addition to its selective action uponthe charge, apparently increases the amount of pitch-like constituentswhich the charge will hold in solution. Where no tar is withdrawn duringthe operation, or where a relatively small amount of tar is withdrawn,the pitch content gradually increases and approaches the saturationpoint, and during the latter portion of the operation, the pitchconcentration may reach and even greatly exceed the saturation point inthe remaining oil of the still charge. Where fresh charging stock isintroduced during the cracking operation, this also assists in holdingthe pitch-like constituents in solution, but as part of the freshcharging stock is crackedand as additional portions of the chargealready in the still are also cracked, the increasedvsolvent efiect ofthe fresh charging stock is overcome and the unvaporized portion of thefresh charging stock also becomes progressively saturated. the improvedprocess of the present invention, part of the pitch-like constituentsproduced during the cracking operation are removed by the action of thebody of fullers earth, and, in some cases, the saturation concentrationor pitch-like constituents in the still charge may also be increased.his latter possibility is apparently due to t e character of thecomponents of the charge removed by the body of fullers earth, and to aselective action of the earth uponcertain of'the constituents of thecharge which .tend to cause rapid precipitation of pitch-likeconstituents and also to the fact that those pitch-like constituents notremoved and remaining in the charge are less injurious. In either batchor semi-continuous operation, the cracking operation is terminated when,or before, the amount of pitch-like constituents remaining in thecharge, above the amount removed by the fullers earth bed and any amountwithdrawn as tar, increases to a point where objectionable depositionwill take place in the heating tubes of the still.

In the process of the present invention, accordingly, both the nature ofasphaltic or pitch-like constituents contained in the charge circulatedthrough the heating tubes is controlled and the amount of suchconstituents or the rate of formation of such constituents is somewhatrestricted, the selective action of the fullers earth removing what weconsider to be the more objectionable constituents and permitting ahigher concentration of less objectionable pitch-like constit ents inthe charge. Such pitch-like constituents as remain in the circulatingcharge, after its passage through the fullers earth bed, and up to thepoint where objectionable deposition begins, we consider to be held insolution in the circulating charge.

In one particularly advantageous way' of carrying out the improvedprocess of the present invention, fullers earth is maintained in theform of a bediextending across the drum or bulk supply tank containingthe main charge-of oil, and the oil is circulated from such drum throughheating tubes and back to the drum. The fullers earth is supported inthe form of a bed through which theentire charge can be circulated, andthe still is rovided with circulating means for circulating the chargethrough the fullefis earth bed. The fullers earth is also sup ported outof contact with the heating surfaces of the still, and provision is madefor circulation of the oil through the heating tubes as well as throughthe fullers earth bed. The circulating charge thus circulated throughthe heating tubes thus contains only the constituents which are notremoved by the circulation through the fullers earth bed. The provisionof a large bed of fullers earth within the pressure still itself has theadvantage that a large surface area of the earth is exposed to thecharge, and a large area of earth bed is rovided for circulation of thecharge theret rough. The pressure still con: structionneed not bechanged by the provision of additional external equipment; but tubularcirculatory pressure still s stems of present day construction can reaily be I provided with a perforated support extend ing across theinterior of the still for supporting the bed of 'earth in contact withthe still charge. The heating tubesmay be either horizontal or vertical,and maybe in either bank or continuous arrangement with mass or streamcirculation. The tube still may thus be one in which there is streamcirculation through a series of tubes in the form of a continuousstream; or the circulation may be in parallel through a large number ofheating tubes. The still may be one in which thermal action is reliedupon to cause the circulation of the charge through the heating tubes,or it may be one in which the circulation through the tubes is efiectedby mechanical means, such as a circulating pump. In such tubular stillsthe'circulation of the charge through the heating tubes and through thebed of fullers earth in the bulk supply tank or drum results in causingall portions of the circulating charge to pass through the bed of earthin the bulk supply tank before they. recirculate through the heatingtubes, while the charge in the bulk supply tank is in contact with alarge area of the fullers earth through which the charge is circulated.

'- The invention will be further described and illustrated in connectionwith the accompany ing drawing which shows in a somewhat conventionaland diagrammatic manner, one form of tubular pressure still embodyingthe invention and adapted for the practice of the process of theinvention; but it is intended and will be understood that the inventionis not limited to the specific construction and operation so described.

In the accompanying drawing, Fig. 1 shows, in a somewhat conventionaland diagrammatic manner, and with part in section and part in elevation,one arrangement of a a tubular pressure still embodying the inventionand adapted for carrying out the process of the invention;

Fig. 2 is a sectional view of the drum or bulk supply tank of Fi 1;

Fig; 3 is an enlarged detailed sectional view of'one form of screensupport by which the fullers earth or like material is supported in thestill; and

Fig. 4 is a similar view of a modified construction of screen support.

The pressure still illustrated comprises the shell or bulk supply'tank 1having an outlet pipe 2 leading to the pump 3 by which the oil is pumpedthrough the lower connecting pipe 4 to the distributing pipes andheaders of the vertical tubes 5. From these tubes the oil and threepasses 9, 10 and 11 separated by baflles for causing the furnace gasesto pass over the vertical tubes in a back and forth manner before.v theyescape through the connecting flue 12 to the stack 13. From'the drum 1of the ressure still a vapor line 14 leads to the re ux tower 15 whichis shown as a ballie tower having a-series of battles v 16 therein.'This tower hasa return pipe 17 leading from the bottom and discharginginto the outlet pipe-2.= The vapor line 18 leads from the tops-of thereflux tower 15 to the condenser 19 from which the condensate anduncondensed gas are c ollectedin the receiver 20. Draw-off pipes 21 and22 are provided for drawing ofi the uncondensed gas and t] 1e condensaterespectively from the receiver 20.

A pressure regulating valve 23 is provided provided; as well as a safetyvalve 28. A

feed line 27 is shown for introducing fresh charging stock into theupper portion of the reflux tower.

forated plates Within the still is provided a perforated support 29suitably secured to the shell of the drum, e. g., by welding, and uponthis perforated screen or support is maintained a relatively deep bodyof .fullers earth or like absorbent material indicated at 31. Across-section of one suitable form of screen support is illustrated inFig. 3. This is made up of live layers, a top layer 32 of e. g. thickplate with perforations, a 4 mesh screen 33, a 40 mesh screen 34,another 4.- mesh screen 33 and another thick steel plate 32 with Aperforations therein. A modified and simpler form of support isillustrated in Fig.4, made up of the upper and lower per- 32 having thescreen 34 between them. The nature of this support can be varied so longas it performs the function of supporting the earth without leakage.lVhere finely divided earth is used, the sup port should be suflicientlyfine to prevent escape of the earth therethrough. We have found itadvantageous, however, to use relatively coarse fullers earth, 0. g.earth of 15 to mesh, in conjunction with a coarser supporting means. Itwill be noted that the perforated support and screen form a floor overthe bottom of the still. \Vith such a screen,

thoroughly sealed by welding or riveting at With a tubular crackingstill of the character illustrated, and with the bulk supply drum about9 ft. in diameter, the perforated floor may advantageously be locatedapproximate 1y 2 ft. above the bottom of the drum, and a bed of fullersearth of for example 10 to 1.8 inches in depth and containing aboutt to7 tons of earth may advantageously be used, although the depth andamount of the earth can be varied.

From Fig. 1 it will be noted that the return pipes 6 extend aconsiderable distance into the drum 1 and terminate in extensions 6discharging to the remote end of the drum from that at which the outlet2 is arranged. Where the velocity of the oil discharged from the pipe 6is such as to cause erosion of the bed of fullers earth, this bed can beprotected by a plate at the point of greatest velocity so as to preventobjectionable erosion.

Inthe operation of the pressure still, and in the carrying out of thecracking process of the present invention therein, the still is chargedand heated to the cracking temperature and pressure. The still may becharged for example through the charging line 36 which may also serve asa tar draw-off at the end of the run. During the cracking operation, theoil is circulated by the circulating pump 3 from the bulk supply tank 1through the connecting pipes 2 and 4 to the heating tubes 5 and thenback through the pipes 6 and 6 to the drum 1, discharging into this drumat the far end. Vapors from the oil are released in the bulk supply tankand pass up through the vapor line 14 into the reflux tower where theheavier ends are condensed by fresh oil introduced into the top of thereflux tower through the feed line 27, and pass with such feed throughthe reflux tower and the run-back line to the pump circulation. Theuncondensed vapors pass through the vapor line from the reflux towerthrough thepressure control valve to the usual condenser and receiver.Additional feed can be introduced through the bearings of the pump bymeans of a feed line 35. The charge is with drawn from the drum belowthe perforated support and is circulated through theheating tubes andback to the drum or bulk supply tank above the perforated support. Theunvaporized portion of the charge, before it can again be withdrawn andpassed through the heating tubes, must pass downwardly through the bedof earth, and the bed of earth thus has an opportunity of exerting itsselective absorbent action upon the objectionable asphaltic orpitch-like constituents of the charge. In the apparatus illustrated itwill be noted that the bed of earth is below the normal liquid level andis completely submerged or immersed in the body of the charge and thatit provides a large surface area in contact with the charge and a largesectional area through which the charge can flow downwardly at arelatively reduced rate as comparedwith the rate of circulation throughthe heating tubes. Ample opportunity is thus provided for the earth toexert its selective absorbent action as the charge is slowly circulatingor filtering downwardly therethrough.

The bed of absorbent material is not, however, relied upon alone to takecare of the pitch-like constituents formed by the cracking operation upto the saturation point, or somewhat beyond the saturation point, in theremaining solvent constituents of the original charge. In the apparatusillustrated it will be noted that the fresh feed introduced through thereflux tower and also the refiuxed vapors from the still are returned tothe outlet pipe 2 from the bulk supply tank and that additional feedvmay be introduced through the pipe 35 and the pump bearings. Thecirculating charge, therefore, is made up of the fresh feed and refluxtogether with such portion of the still charge itself as percolatesdownwardly through the bed of absorbent material. The-oil aftercirculation through the heating tubes is discharged into ent materialpart of the pitch-laden oil content of the charge increases.

The absorbent action of fullers earth or like material is such that anincreased percentage of the charge, includin any fresh oil introducedduring the operations, can be taken off as pressure distillate, and thepitch- I content of the circulating charge can be carried to anincreased amount during the run without objectionable carbon deposit onthe heating tubes. As the pitch content of the charge approachessaturation, the removal from the clrculating charge of the constituentswhich are removed by the fullers earth prolongs the period of operationpreceding saturation and enables the operation to be continued for amuch longer-period of time without objectionable carbon deposit on theheating tubes. Even where the pitch content is carried to a pointconsiderably above saturation, the fullers earth will remove from thecirculating charge objectionable constituents which would otherwise tendto separate out in the heating tubes.

The fullers earth of commerce is obtained in varying degrees offineness. The finest grades of earth such as are commonly used for oilrefining, are not so well adapted for use in the process of the presentinvention as the coarser grades, e. g., from 15 to 30 mesh, which permitready flow of the circulating oil therethrough, and which do not tend toleak through the supportin screen and enter the circulating stream ofoil We have found Olmstead earth of 1530 mesh well adapted for use inthe process of the invention. Fullers earth is of a clay-like character,and may be considered as an absorbent clay. Other absorbent clays havingsimilar properties can similarly be used in the process of theinvention. In so far as the action of the fullers earth is a filteringaction in which the earth absorbs or otherwise holds particles ofcolloidal carbon or asphaltic constituents, etc., thus removing themfrom the cir culating charge, other filtering materials can be used toobtain similar results. Other absorbent materials, having a similarselective absorbent action upon the objectionable asphaltic orpitch-like constituents of the circulating charge can also be used. Soalso, from the standpoint of the desulfurizing action of the fullersearth, other porous or finely divided materials having a similardesulfurizing action can be used to remove or assist in removin in aselective manner the objectionable sul ur-containing constituents of thecirculating charge, for example, silica Our use of fullers earthindicates it to el %e a particularly advantageous material foruse in theprocess of the invention, inasmuch as it appears to combine in itselfvaluable filtering, selective absorbent, desulfurizing and otherproperties which favorably affect and benefit the pressure stilloperation.

In carrying out arun according to the present invention, the still canbe charged with fresh chargin stock in the usual way. The charging stocmay, for example, be gas oil or other suitable charging stock which isto be cracked for the production of gaso line or pressure distillatetherefrom. The still charge is brought to the required crackingtemperature and pressure in the usual manner. After the crackingtemperature is reached, cracking begins and takes place in a gradual andprogressive manner, the lighter vapors forming the pressure distillatepassing off and being removed from the still, while the heavier vaporsare refluxed back to the still. The asphaltic or pitch-like constituentsformed are in part absorbed by the fullers earth and in part held insolution in the remaining constituents of the charge. As the reactionproceeds the unabsorbed pitch constituents continue to dissolve in theoil and progressively approach, or pass, the saturation point. Fresh oilmay be introduced as the operation progresses, and the solvent capacityof fresh oil so introduced further assists in holding the unabsorbedpitch constituents in solution. The action of the absorbent material mayalso be supplemented by Withdrawing part of the pitch laden oil formedby the cracking reaction as the operation progresses. For example, apart of the pitch laden oil may be withdrawn during the period justpreceding the time at which the pitch concentration reaches thesaturation point, and the withdrawal of tar may be continued for all orpart of the remaining period of operation until the operation isterminated. A

Fullers earth has been found to be a particularly advantageous materialto use in the process of the present invention. It can advantageously becharged into the still in an uncalcined condition, and the earth will bedehydrated during the bringing up of the still to cracking conditions,and the water present in the earth'will be driven off along with thedrips before the still reaches cracking conditions. Calcined earth canhowever be used. A bed of fullers earth approximately 10 to 18 inchesdeep has been found satisfactory.

It will be evident that the pressure maintained during the crackingoperation can vary, depending upon the character of the charging stockand other considerations. For example, with a gas oil charging stock, apressure up to to lbs. per square inch or even up to 125 lbs. or morecan be used. With a lighter kerosene charging stock, a higher pressure,e. g. from'up to 125 lbs. to around 300 lbs. or more can be used withadvantage. The pressure can be regulated by a pressure reducing valvemaintained between the still and condenser, or the condenser canlikewise be maintained under still III I pressure, and the pressureregulating valve at the outlet of the receiver.

The character of the charging stock used in the process can also bevaried. In particular, a charging stock which contains constituentswhich otherwise would tend to cause an increased deposit of carbon orcoke on the heating surfaces can be used in the process and theapparatus of the present invention. and their objectionable tendencyovercome or greatly reduced, owing to the selective or preferentialabsorption of such impurities by the fullers earth bed.

The following is an example of the practice of the present invention ascarried out in a still of the character illustrated in the drawing:

The fullers earth used was Olmstead fullers earth of 16 to mesh and thestill was charged with 7 tons of the raw earth forming a bedapproximately 18 inches deep on a perforated support of the characterillustrated which was arranged approximately 2 feet above the bottom ofthe drum, the drum being about 9'feet in diameter and about'31.6 feetlong. I. The still was charged with 8000 gallons of gas oil chargingstock. The still charge was heated, drips were taken off, and

. the charge was brought to a working pressure of about 125 pounds. Thestill was then opened to the condenser and the distillate began to passover. At about the same time or shortly thereafter, the introduction offresh charging stock into the still through the reflux tower Was begun,the amount correspondin approximately to about 115% of the overheaddistillate taken ofl. The rate of distillate taken off was about 820gallons an hour, and the rate of feed through the tower was about 940 to950 gallons an hour. During the run, tar was withdrawn at a ratecorresponding approximately to about 15% of the overhead distillate. Therate of circulation through the heating tubes was about 2000 gallons aminute. About 31,000 gallons of pressure distillate of 47.5 Baum ravitywas obtained from a throughput or about 43,700 gallons representing ayieldof about 71% of the. charge as pressure distillate.

Where the Withdrawal of tar, even though in relatively small amount, isomitted the period during which the operation can be carried out withoutobjectionable carbon deposit is somewhat reduced. The operation ispreferably conducted to a. point such that the charge remaining in thestill can be withdrawn in a fluid condition. Where the operation hasbeen carried to a point such that the unabsorbed pitch in the oilmaterially exceeds the saturation point, part of the pitch-likeconstituents present in the remaining charge will be in solution andpart in suspension.

In carrying out the process of the invention, an increased percentage ofthe charging can be taken off as distillate, the fullers earthinhibiting the formation of objectionable carbon deposit. When the stillis operated to obtain a higher percentage of the charge off asdistillate, a somewhat more unsaturated product may be obtained and the'amount of tar to be drawn off and to be redistilled or otherwise treatedor disposed of will be less. In some cases, further treatment of the tarmay be avoided. With higher prcentages ofthe charge off as distillate,

less heat is required in heating up the additional stock and more heatis available for cracking. With higher, percentages of the charge off asdistillate, a material saving in fuel may be effected, due to thegreater percentage of distillate and also due to the decrease in timerequired to bring the still to cracking conditions of temperature andpressure for a given amount of char e. Where the tar i redistilled, afarther savmg in fuel is effected, due to the decreased amount of tarwithdrawn.

per day, while at the same time ro onging the run and reducing theproportlon of time now lost for shutting down and cleaning, anddecreasing the fuel consumption.

We have used the same bed of earth in successive runs, with removal ofonly a few inches of the top layer and replacement of it with a freshlayer of earth. After continued use, however, the fullers earth becomesspent or exhausted, and must be replaced by fresh earth. The spent earthcan be regenerated, or may be otherwise utilized or disposed of.

The gasoline production can in this way be greatly increased er stillWhen a run is terminated, and the charge has been withdrawn and thestill steamed out, we have found the top of the earth covered with athin layer or crust composed of earth and pitch or coke, with the earthbed underneath dry and granular.

In the process of the present invention, the entire body of the chargingstock and of the .still charge is relied upon to hold in solution,

until e saturation point is'reached, such 'of the pitch-like orasphaltic constituents,

still charge for such pitch-like constituents- -will progressivelydecrease until saturation is reached. The operation is preferablyterminated when the concentration of pitchlike constituents present inthe charge exceeds .ture in a circulatory pressure still in which theoil is heated to a cracking temperature in a tubular heater, whichcomprises maintaining in said still charge a body of fullers earth on asupport adapted to permit free passage of oil and extending entirelacross the charge of oil in the pressure sti l, withdrawing oil frombeneath said supportand discharging the oil directly int-o the charge ofoil above said support and the material supported thereon, andcontinuing the operation until the pitch content of the still chargebuilds up at least to saturation.

2. The improvement in the cracking of hydrocarbon oils by distilling acharge of the oil under pressure at a cracking temperature in acirculatory pressure still in which the oil is heated to a crackingtemperature in a tubular heater, which comprises maintaining in saidstill charge a body of absorbent material on a support adapted to permitfree passage of oil and extending entirely across the charge of oil inthe pressure still,

withdrawing oil from beneath'said support and discharging the oildirectly into the charge of oil above said support and the materialsupported thereon, and continuing the operation until the pitch contentof the still charge builds up at least to saturation.

3. The improvement in the cracking of hydrocarbon oils by distillin acharge of the oil under pressure at a crac ing temperature in acirculatory pressure still .in which the oil is heated to a crackingtemperature in a tubular heater, which comprises maintaining in saidstill charge a body of filtering material on a support adapted to permitfree passage of oil and extending entirely across the charge of oil inthe pressure still, withdrawing oil from beneath said support anddischar ing the oil directly into the charge of oil a ove said supportand the material supported thereon, and continuing the operation untilthe'pitch content of the still charge builds up at least to saturation.

4. The improvement in the cracking of hydrocarbon oils by distillin acharge of the oil under pressure at a crac ing temperature in acirculatory pressure still in which the oil is heated to a crackingtemperature in a tubular heater, which comprises maintaining in saidstill charge a body of desulfurizing material on a support adapted topermit free passage of oil and extending entirel across the charge ofoil in the pressure stil withdrawing oil from beneath said support anddischarging the oil. directly into the charge of oil above said supportand the material supported thereon, and continuing the operation untilthe pitch content of the still charge builds up at least to saturation.

5. The improvement in the cracking of hydrocarbon oils by distilling acharge of the oil under pressure at a cracking temperature in acirculatory pressure still in which the oil is heated to a crackingtemperature in a tubular heater, which comprises maintaining in saidstill charge a body of fullers earth on a' support adapted to permitfree passage of oil and extending entirely across the charge of oil inthe pressure still, withdrawing oil from beneath said support anddischar ing the oil directly into the charge of oil a ove said supportand the material supported thereon, feeding fresh oil to the pressurestill,

and continuing the operation until the pitch content of the still chargebuilds up at least to saturation.

6. The improvement in the cracking of hydrocarbon oils by distilling acharge 0 the oil under pressure at a crackmg temperature in acirculatory pressure still in which the oil is heated to a crackingtemperature in a tubular heater, which comprises maintaining in saidstill charge a body of fullers earth on a support adapted to permit freepassage of oil and extending entirely across the charge of oil in thepressure still, withdrawing oil from beneath said support anddischarging the oil directly into t e charge of oil above said supportand the material supported thereon, withdrawing pitch-laden oil from thepressure still and continuing the operation while controlling thewithdrawal of pitch-laden oil to cause the pitch content of the stillcharge to build up at least to saturation. i

7. The improvement in the cracking of by drocarbon oils by distilling acharge of the oil under pressure at a cracking temperature in acirculatory pressure still in which the oil is heated to a crackingtemperature in a tubular heater, which comprises maintaining in saidstill charge a body of fullers earth on a support adapted to permit freepassage of oil and extending entirely across the charge of oil in thepressure still, withdrawing oil from beneath said support anddischarging the oil directly into the charge of oil above said supportand the material supported thereon, feeding fresh oil-to and wit drawingpitch-laden oil from the pressure still, and continuing the operationwhile controlling the feed of fresh oil and withdrawal 8. Theimprovement in the cracking of hydrocarbon oils by distilling a chargeof the oil under pressure at a cracking tem erature in acirculatorypressure still in w ich the oil is heated to a cracking temperature in atubular heater, which comprises maintaining in said still charge a bodyof fullers earth on a support adapted to permit free passage of oil andextending entirely across the charge of oil in the pressure still,withdraw.

ing oilfrom beneath said support and dis charging the oil directly intothe charge of oil above said support and the material supported thereon,and continuing the operation until the pitch content of the still chargeexceeds saturation.

' the oil directly into the charge of oil above said support and thematerial supported thereon, continuing the distillation until the pitchcontent of the still charge builds up at still while in a fluidcondition.

supply tank a body least to saturation and thereafter withdrawing theremaining charge from the 101 The improvement in the cracking ofhydrocarbon 'oils under pressure in circulatory pressure stills'in whichthe oil is heated to acracking temperature in a tubular heater,

which comprises circulating the still charge of oil froma drum or bulksupply tank, through heating tubes and back to the drum or bulk supplytank, distilling the circulating oil under pressure and at a crackingtemperature, maintaining in the drum or bulk of fullers earth, supportedin the still charge upon a support adapted topermit free passage of oiland extending entirely across the charge of oil in the drum or bulksupply tank and dividing the same into upperand lower compartments,withdrawing the oil from the lower compartment below said support anddischarg.

ing the oil from the heating tubes directly into the upper compartmentabove said support and the material supported thereon, and

pressure I continuing the distillation until the pitchcontent of thestill charge builds up at least to saturation.

In testimony whereof we aflix our signatures.

EUGENE C. HERTHEL. HARRY L. PELZER.

